<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    * {
      box-sizing: border-box;
    }

    *:before, *:after {
      box-sizing: inherit;
    }

    body {
      width: 100%;
      height: 100%;
      font-size: 100%;
      line-height: 1.5;
    }

    .example {
      width: 100%;
      height: 100vh;
      max-width: 1200px;
      margin: 0 auto;
      padding: 1em;
      display: flex;
      flex-direction: column;
      align-items: center;
    }

    .circle {
      width: 100px;
      height: 100px;
      border-radius: 50%;
    }

    .red {
      background-color: darkred;
    }

    .blue {
      background-color: lightblue;
    }

    .pink {
      background-color: darksalmon;
    }
  </style>
</head>
<body>
  <div class="example">
    <div class="circle red"></div>
    <div class="circle blue"></div>
    <div class="circle pink"></div>
  </div>
</body>
</html>